Alkaline Phosphates And Silicates Halogen Cheap Broadband Luminescence Properties Of Bismuth Ions And The Formation Mechanism

In2001, Fujimoto et al. discovered the broadband near infrared (NIR) emission ranging from1000to1600nm in bismuth doped aluminosilicate glass. Since the luminescent properties having potential applications in optical fiber communications and tunable laser, it has attracted great interest on the luminescent property of Bi ion by domestic and foreign scholars again. Followed by the next decade, a large number of Bi doped glass matrixes, such as silicates, germanate, phosphates and borates, and crystal matrixes have been reported. Compared with rare earth luminescent center, it shows broadband emission, high emitting efficiency and long flourescence lifetime due to the the electron configuration feature of Bi ion. In addition, different from transition metal luminescent center, the effect of crystal field strengh and ligand field environment for Bi ion is not strong, and it has good adaptability and choice for the matrix. Moreover, with limited rare earth resources decreasing, the main group metal Bi ion will play more and more important role in luminescent center due to the excellent luminescent property.However, compared to the well-known Bi3+, the energy level structure, formation mechaism and luminescent mechanism of low valence Bi ion are not clear and still lack of convincing theoretical basis. The luminescent property of low valence Bi ion is not only affected by many external factors, such as the crystal field strengh, ligand field environment and lattice size and so on, also depends on the ionic valence state, such as Bi2+, Bi+and Bi0. Therefore, exploring material structure on the influence and formation of broadband luminescent properties for low valence Bi ion will contribute to the understanding of broadband luminescent mechanism for Bi ion, for the design and preparation of new type of Bi active ultra-broadband luminescent materials to provide effective theoretical and experimental basis. Hence, alkaline earth halide phosphate and silicate crystal materials were used as matrixes, to investigate the relationship between the broadband luminescent properties of Bi ions and the structure of matrix, and discuss the broadband luminescent properties, luminescent mechanism and formation mechanism of different valence state Bi ion.Firstly, we have investigated the effect of preparation atmosphere on the luminescent property of Bi ion. Bi3+was reduced to Bi+by H2gas in Bas(PO4)3Cl lattice, yellow-white and NIR emissions from Bi+were observed at the excitation of227and690nm, respectively, but there is no emission in air atmosphere. Results show that the low valence Bi ion is reduced by reductive atmosphere and the luminescent mechanism of Bi3+as well as Bi+have been discussed based on photoluminescence.Secondly, the relationship between the lattice size and luminescent property of Bi has been investigated. In M5(PO4)3Cl lattice, only the radius of matrix cation, which close to Bi+, can be accommodated by Bi+, since the radius of Ba2+close to Bi+, thus Bi+was generated only in Ba5(PO4)3Cl lattice, while Sr5(PO4)3Cl and Ca5(PO4)3Cl were not. Results show that the valence state of Bi ion is indirectly controled by the lattice size and eventually leads to the differences of luminescent properties.Thirdly, the effect of ligand field environment on low valence Bi ion has been investigated. the coordination environment of Bi3+was changed by introducing larger electronagativity of F ion into the Ca5(PO4)3Cl lattice, eventually induced Bi3+reduced to Bi2+, and orange-yellow emission (521nm) was observed from Bi2+. The luminescent mechanism of Bi2+has been dicsussed.Finally, we also have investigated the effect of crystal field strengh on the luminescent properties of Bi. The vacancy defects were generated by different valence ion codoping into Ba2MgSi2O7lattice, which substituted for Ba2+site, inducing luminescent center reduced from Bi3+to Bi+and broadband green emission (500nm) was observed at the excitation of344nm. On the basis, we also adjust the crystal field strengh by changing the parameters of cell size to realize the emission peak blue-shift, and the luminescent mechanism of Bi+has been discussed. Furthermore, green long afterglow emission from Bi+was discovered for the first time and Bi+is a novel type of long afterglow luminescent center.